Multi-physics Coupling Analysis And Experimental Study Of A Novel MOCVD Reactor

Recently, with the development of semiconductor materials and manufacturing technology, Group ? nitrides, especially gallium nitride (GaN), have been widely used in high-power optoelectronic devices, such as field effect transistors (FETs), ultraviolet (UV) detectors, laser diodes (LDs), solar cells, high-temperature sensors, and light-emitting diodes (LEDs) because of its wide band-gap and high thermal conductivity. However, metal-organic chemical vapor deposition (MOCVD) device is the most popular equipment to grow Group ? nitrides, including high-quality GaN epitaxial layers for blue LED application. At present, production type MOCVD equipments in China are almostly monopolized by foreign manufacturers due to the lack of systematic theoretical and experimental support in the design of the reactor, which has seriously hampered the development of China's semiconductor manufacturing industry, so the research and industrialization of homemade production type MOCVD equipment is received widespread attention from academia and industry world. In this thesis, we focus on the localization of the MOCVD device, and study the new designed Buffered Distributed Spray (BDS) MOCVD reactor.A novel kind of BDS MOCVD reactor design was presented to ensure uniform and stable flow field. The combination of vertical flow from the distributed showerhead injector nozzles and three horizontal flows from reactor center has many advantages. First, such combination can suppress the flow and thermal recirculation effectively, and the process is directly scaleable between reactor sizes with keeping uniform growth rate and laminar flow distribution. Moreover, it provides hardware basis for wide range of MOCVD process parameters and the optimization of the processing window.With the combination of fluid flow, heat transfer, mass transfer and chemical reaction kinetics, the multi-physics coupling model of GaN epitaxy in MOCVD reactor was studied. And the multi-physics coupling model was established to investigate how reactor geometry affect flow field, and concentration distribution, growth rate and its uniformity in BDS reactor with finite volume method(FVM) method. At the same time, the experimental results were carried out. The results show that the model can correctly reflect the actual situation of GaN epitaxial growth rate. Then, the BDS reactor design was confirmed to be feasible by comparison, and simulation analysis. In addition, simulation and experiment analysis were conducted to study the influence of flow rate, process pressure and carrier rotational speed on the GaN growth rate and uniformity in the BDS reactor, and the mechanisms of the influences of these parameters were analyzed with multi-physics couppling phenomenon. Finally, the scalability of the BDS reactor was analyzed by simulation. The results show that the BDS structure has good scalability and can be further upgraded and expanded, which is suitable for the capacity and size needs of MOCVD equipment.In this work, for the first time, the non-uniformity and its changing law in GaN MOCVD growth under different processing conditions were analyzed, summarized and explained, so as to provide guidance for the exploration of the optimal epitaxy process parameters.Finally, a LED epitaxy structure was growth in the BDS reactor installed in a MOCVD experimental platform. And the elment composition, phase composition, morphology and PL film thickness and wavelength of the LED structure were carried out with SIMS, XRD, TEM and PL tests. Experimental results show that quality of the fabricated films is excellent, and which proves good performance of the novel BDS reactor design, especially in the multi quantum wells(MQWs) structure growth, and which shows good application prospect and research value. On the other hand, PL film thickness and wavelength inhomogeneities between different radius positions also show that the BDS reactor needs to be further improved, such as the gas mixing mode in the center region and the way to reduce flow inlet or optimize the gas flow direction, to limts the fully mixed gases as close as possible to the central position.